Coriolis-relieving aircraft rotor assembly

ABSTRACT

In a multiple blade tail rotor of a helicopter, cyclic Coriolis forces are cushioned by resilient stress-absorbing means interposed between the engine output member and the pairs of trunnions on the teetering axes of the blade hubs to permit the pairs of trunnions to oscillate relative to each other and relative to the engine output member.

United States Patent 11 1 1111 3,784,319 Amer et al. Jan. 8, 1974CORIOLIS-RELIEVING AIRCRAFT ROTOR 3,156,302 11/1964 Jordan 416/148ASSEMBLY 3,193,019 7/1965 Drees et al r 416/102 X 3,637,321 1/1972Nekrasov et aLm 416/131 X 1 1 Inventors: Kenneth Amer, Los g 3,667,8636/1972 Brenner 416/135 ux Howard T. Lund, Playa Del Ray, 3,700,351 101972 Flux 416/198 x bmh FOREIGN PATENTS OR APPLICATIONS [73] Assign:Summa Cmlmrafim, Culver City 726,828 3/1932 France 416/135 Calif-247,395 5 1912 Germany 416 135 p 7, Great Britain .1 [21] APPL 244,427Primary ExaminerEverette A. Powell, Jr.

Alt0rney-Jess M. Roberts et a1. [52] Cl. 416/135, 416/148 [51] Int. Cl.B64c 27/52 57 ABSTRACT [58] Field of Search 4l6llilglll3o5z, 112478, Ina multiple blade tail rotor of a helicopter Cyclic Coriolis forces arecushioned by resilient stressabsorbing means interposed between theengine out- [56] References Clted put member and the pairs of trunnionson the teeter- UNITED STATES PATENTS ing axes of the blade hubs topermit the pairs of trunr ,3 2/l950 Hunt n 1 nions to oscillate relativeto each other and relative to 2,961,051 11/1960 Wilford et al 416/131 xthe engine output member 3,026,942 3/1962 Cresap 1 416/135 X 3,087,6904/1963 Doman et a1. 416/102 X 13 Claims, 7 Drawing; Figures PATENTEU JAN74 SMET 2 (IF 3 1 CORIOLIS-RELIEVING AIRCRAFT ROTOR ASSEMBLY BACKGROUNDOF THE INVENTION In a relatively simple helicopter tail rotor assembly asingle pair of diametrically opposite blades are mounted on a common hubthat is formed with a pair of trunnions and the pair of trunnions definea teetering axis that is at an acute angle to the axis of the blades.Such a two-bladed teetering blade rotor is both simple and reliable. Itdoes not require bearings which must oscillate on each revolution of therotor and at the same time carry the full centrifugal force of theblades. In addition, it relieves the potentially powerful Coriolis"torques merely by deflection of its drive system in torsion twice oneach revolution of the rotor.

The trend, however, is toward multiple-bladed teetering tail rotors inwhich two or more pairs of diametrically opposite blades are mountedcorresponding pairs of trunnions for rotation in spaced planes with themultiple blades actuated by a common drive shaft. Unfortunately, sincethe cyclic Coriolis torques created by the pairs of blades are out ofphase with each other, such a drive system is incapable of inherentlyrelieving the torques.

An example is a teetering tail rotor wherein two pairs of diametricallyopposite blades are mounted on two corresponding pairs of trunnions withthe pairs of blades at an angle relative to each other of 60 or 90.Whenever the rotor experiences first harmonic flapping, one of the pairsof blades tries to speed up at the same instant in time that the otherpair of blades tries to slow down. Thus, the two pairs of blades try tomove cyclically like a pair of scissors and the consequent highmagnitude stresses occurring twice on each revolution are concentratedin a short portion of the common drive shaft. If these powerful stressesare not relieved, the drive shaft may fatigue to the point of structuralfailure.

SUMMARY OF THE INVENTION The problem of Coriolis relief in amultiple-blade tail rotor is solved by interposing resilientstress-absorbing means between the engine output and each of the pairsof trunnions of the hub assembly.

In one embodiment of the invention under this generic concept, the hubassembly of the rotor has a base portion that is fixed to the driveshaft and a pair of arms integral with the base portion extend onopposite sides of the shaft from the base portion to each of themultiple pairs of trunnions. The base portion of the. hub assembly isrelatively rigid but the integral pairs of arms are relatively flexibleto permit the individual pairs of trunnions to oscillate relative toeach other and relative to the common drive shaft. The pairs of armsprovide sufficient torsional resiliency to reduce the cyclic Coriolistorques to non-destructive levels while possessing sufficient strengthto transmit the maximum driving torques as well as to carry other staticand dynamic loads.

This first embodiment of the invention has the simplicity of atwo-bladed teetering rotor in that no onceper-revolution cyclic bladepitch change occurs since the pitch control arms are located on theteetering axis. Two pairs of diametrically opposite blades on a singledrive shaft do not require any additional bearingsor mechanicalcomplexity over that required by two rotors each of which has a singlepair of diametrically opposite blades. v

The hub assembly of a second embodiment of the invention also has a baseportion with pairs of arms extending therefrom to corresponding pairs oftrunnions but in this instance the pairs of arms are relatively rigidbut the base portion is of yielding construction to permit the rigidarms to oscillate in response to cyclic Co riolis forces. Thus, therigid arms tilt as required for independent oscillation of the pairs oftrunnions relative to the drive shaft on which the hub assembly ismounted.

The yielding base portion of the hub assembly includes a hub with adiametrical pair of integral spokes extending radially from the hub. Tworelatively rigid structures are integral with the outer ends of the twospokes respectively and the two rigid structures are integrallyinterconnected by two webs with the two rigid structures and the twowebs extending continuously circumferentially around the hub structure.With the blades of the rotor mounted on two pairs of trunnions, each ofthe rigid portions of the hub assembly is connected to one trunnion ofeach of the two pairs. The two spokes are resiliently yieldable intorsion and the two interconnecting webs are resiliently flexible topermit the two rigid portions of the hub assembly to rock oppositelyrelative to each other for oscillation of the two pairs of trunnionsrelative to each other and relative to the shaft on which the hubassembly is mounted.

A third embodiment of the invention is a rotor which two pairs ofdiametrically opposite blades mounted on two corresponding trunnionsthat are driven by two corresponding shafts in the form of a pair ofconcentric torque tubes. Each of the concentric torque tubes flexesresiliently in torque to permit the pair of trunnions thereon tooscillate independently relative to the engine output member to whichboth torque tubes are connected.

The features and advantages of the invention may be understood from thefollowing detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings,,which are to beregarded as merely illustrative:

FIG. 1 is a fragmentary perspective view illustrating the firstembodiment of the invention; a

FIG. 2 is a perspective view of a hub structure that is employed in thefirst embodiment of the invention;

FIGS. 3, 4, and 5 are perspective views of a hub structure employed in asecond embodiment of the invention; I FIG. 6 is a fragmentary sectionillustrating a third embodiment of the invention; and

FIG. 7 is a transverse section taken as indicated by the line 7 7 ofFIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION In theembodiment of the invention shown in FIG; 1, a tail rotor of ahelicopter has a pair of diametrically opposite blades 20 and 21 in anouter plane of rotation and a second pair of diametrically oppositeblades 22 and 23 rotating in an inner plane. In a well known manner theroots or shanks of the two blades 20 and 21 are mounted in acorresponding diametrically opposite tubular shanks 24 of a hub 25 withthe two blades rotatable about their axes as required for changes inpitch. In like manner the two blades 22 and 23 are rotatably mounted inthe tubular shanks 26 of a hub 28. The two pairs of blades arepositioned at an angle relative to each other with the consequency thatthe cyclic Coriolis torques created by the two pairs of blades are outof phase with each other.

The hub that carries the two outer blades 20 and 21 is formed with apair of opposite trunnions 30 by means of which it is mounted to teeterabout a transverse axis that is non-perpendicular to the pitch axis ofthe two blades. In like manner the hub 28 that carries the inner pair ofblades 22 and 23 is formed with a pair of opposite trunnions 32.

The two pairs of blades are mounted on a common engine output member inthe form of a drive shaft 34 that is journaled in a gearcase 35 and awell known mechanism is provided for changing the pitch of the fourblades by remote control. In the construction shown, the pitch controlmechanism includes the usual swashplate 36 that is slidable on a splinedportion 38 of the drive shaft 34 and the swashplate is controlled by abell crank 40 that is mounted by a pivot 42 on the gearcase 35. One armof the bell crank 40 is connected to the swashplate 36 by pivot means 44and the second arm of the bell crank is connected by pivot means 45 to acontrol rod 46.

A pair of relatively short links 48 are connected at their inner ends tothe swashplate 36 by corresponding pivots 50 and at their outer ends areconnected by pivots 52 to corresponding pitch control arms 54 of the twoblades 22 and 23, respectively. In like manner a pair of relatively longlinks 55 are connected to the swashplate by corresponding pivots 56 withthe outer ends of the links connected by pivots 58 to pitch control arms60 of the two outer blades 20 and 21, respectively. The two pitchcontrol arms 60 are shown in FIG. 1.

The structure in FIG. 1 described to this point is more or lessconventional and taught by the prior art. The novel feature of thisfirst embodiment of the invention is a hub structure, generallydesignated 62, that is best shown in FIG. 2 and which serves as meansfor pivotally mounting the two pairs of trunnions 30 and 32 on the driveshaft 34. The hub structure 62 has a base portion 64 which is keyed tothe drive shaft 34 and has two pairs of integral arms comprising arelatively long pair 65 equipped with self-aligning bearings 66 tojournal the pair of trunnions 30 of the pair of blades 20 and 21 and arelatively short pair of arms 68 with similar bearings 70 to journal thetrunnions 32 of the pair of blades 22, 23. Both of the pairs of arms areof adequate strength to drive the rotor blades but nevertheless at leastone of the two pairs of arms is sufficiently resilient to flex inresponse to the cyclic Coriolis forces and thus serve asstress-absorbing means to avoid excessive stessing of the drive shaft.In this instance, both of the pairs of arms 65 and 68 are resilientlyflexible to permit oscillation of the two pairs of trunnions 30 and 32relative to each other and relative to the drive shaft 34. As shown inFIG. 2, the ends of the pair of shorter arms 68 may be interconnected byan angular plate 72.

A second embodiment of the invention incorporates a hub structure,generally designated in FIGS. 3, 4, and 5 which is substituted for thehub structure 62 of the first embodiment of the invention. In most otherrespects the second embodiment is largely identical to the firstembodiment.

The hub structure 75 has a central base portion 76 in the form ofa hubthat is keyed to the drive shaft 34. Integral with the base portion orhub 76 is a pair of diametrically opposite radial spokes 78 whichpreferably are of noncircular cross-sectional configuration as shown.Integral with the outer ends of the two spokes 78 respectively are rigidportions 80 of the hub structure and the two rigid portions 80 areintegrally interconnected by relatively thin webs 82 of metal, the tworigid portions and the two webs being continuous around thecircumference of the hub structure. Each of the two rigid portions 80 ofthe hub structure has an upwardly extending arm 84 equipped with aself-aligning bearing 85 to journal one of the upper trunnions 30 andhas a second similar donwardly extending arm equipped with aself-aligning bearing 88 to journal a corresponding one of the pair oflower trunnions 32.

The two pairs of arms 84 and 86 are rigid, being rigid parts of the tworigid portions 80 of the hub structure but the base portion of the hubstructure comprising the pair of spokes 78 and the pair of thin webs 82is resiliently yieldable to permit the arms to tilt as required foroscillation of the two pairs of trunnions relative to each other andrelative to the drive shaft 34. The resilience of the base portion ofthe hub structure is provided in part by resilience in torque of the twospokes 78 and in part by resilience in flexure of the two thin webs 82.Thus, to permit oscillation of the upper pair of bearings 85 relative tothe lower pair of bearings 88 and to permit oscillation of both pairs ofbearings relative to the hub 76, the two spokes 78 yield oppositely intorque to permit the two rigid portions 80 of the hub structure to rockin opposite directions and the two thin webs 82 bow in a resilientmanner to accommodate the opposite rocking of the two rigid portions 80.

The construction of the third embodiment of the invention may beunderstood by reference to FIGS. 6 and 7.

In FIG. 6 the engine output member to which the two pairs of trunnionsare connected in a bevel gear 90 in a fixed casing 92, the bevel gearbeing actuated by a second bevel gear 94 on an engine-driven shaft 96that is journaled in a bearing 98. The bevel gear 90 is unitary with anouter tubular drive shaft 100 that is journaled in a bearing 102. Theouter end of the outer tubular shaft 100 is provided with a collar 103that forms a pair of diametrically opposite trunnions 104 which arejournaled in corresponding bearing sleeves 105 of a hub 106 that carriesa pair of diametrically opposite rotor blades 108 (FIG. 7). Each of thetwo blades 108 has the usual pitch control arm 110 that is operated by acorresponding link 1 12. The pair of diametrically opposite blades 108rotate in an inner plane and a second pair of diametrically oppositeblades (not shown) 1'0 tate in an outer plane.

The second pair of diametrically opposite blades are mounted ontrunnions (not shown) that are formed by a collar 114 that is unitarywith an inner tubular drive shaft 115. The inner tubular shaft 115 isconcentric to the outer tubular shaft 100 and is fixedly interlockedwith the outer tubular shaft by mutually engaged splines 116 on the twoshafts near the inner ends thereof. The inner end of the inner tubularshaft 115 is journaled in a thrust bearing 118 inside the casing 92.

It is apparent that both of the two tubular shafts 100 and 115 arefixedly connected at their inner ends to the engine output member orbevel gear 90 and it is further apparent that both function as resilienttorque tubes which may yield in torque independently of each other inresponse to the cyclic Coriolis forces. Thus, the two torque tubespermit the two pairs of trunnions to oscillate relative to each otherand relative to the bevel gear 90.

Our description in specific detail of the selected embodiments of theinvention will suggest various changes, substitutions, and otherdepartures from our disclosure within the spirit and scope of theappended claims.

What is claimed is:

1. An aircraft rotor structure comprising:

at least two pairs of diametrically opposite blades;

an engine output member;

at least two pairs of trunnions rotationally driven by the engine outputmember with each pair of diametrically opposite blades pivoted on atrunnion pair for teetering movement, and

stress absorbing means interposed between the output member and thepairs of trunnions to permit relative rotational movement between thetrunnion pairs in relieving coriolis forces resulting from the teeteringmovement of the diametrically opposite blades.

2. The aircraft rotor structure of claim 1 wherein the means providingrelative rotational movement between the trunnion pairs permits relativerotational movement between each of the trunnion pairs and the engineoutput member.

3. The aircraft rotor structure of claim 1 wherein said means to permitrelative rotational movement between the trunnion pairs includes:

a hub having a base portion which is relatively rigid;

said base portion being connected directly to the engine output member;

arms formed integrally with the base portion with an arm extending fromthe base portion to each trunnion pair; each arm having sufficientstrength to transmit rotational movement from said base portion to atrunnion pair to provide rotational movement of the diametricallyopposite blades pivotally connected to the trunnion pair, and

at least one arm being sufficiently resilient to permit relativerotational movement of the trunnion pair to which the arm is connectedwith respect to the axis of theengine output member,

whereby relative rotational movement between the trunnion pairs ispermitted and also relative rotational movement of at least one trunnionpair with respect to the axis of the engine output member in reducingthe transmission of coriolis forces to the engine output member.

4. The aircraft rotor structure of claim 3 wherein the connection ofeach arm to a trunnion pair is transverse to the plane within which thediametrically opposite blades teeter with respect to the trunnion pair.

5. The aircraft rotor structure of claim 3 wherein each arm issufficiently resilient to permit relative rotational movement of eachtrunnion pair relative to the axis of the engine output member.

6. The aircraft rotor structure of claim 4 wherein each arm issufficiently resilient to permit relative rotational movement of eachtrunnion pair relative to the axis of the engine output member.

7. The aircraft rotor structure of claim 3 wherein a pair of armsextends from the base portion to each trunnion pair.

8. The aircraft rotor structure of claim 7 wherein the connections ofeach pair of arms to each trunnion pair are transverse to the planewithin which the diametrically opposite blades teeter with respect tothe trunnion pair.

9. The aircraft rotor structure of claim 1 wherein the means providingrelative rotational movement between the trunnion pairs includes:

a hub structure having a base portion driven by the output member and apair of arms unitary with the base portion extending from the baseportion to two trunnion pairs positioned! on opposite sides of the axisof the output member,

said arms being relatively rigid, and

said base portion having sufficient strength to transmit rotationalmovement to the trunnion pairs but being resiliently deformable to allowthe two arms to tilt relative to the axis of the output member to permitthe trunnion pairs to undergo relative rotational movement and for eachtrunnion pair to undergo relative rotational movement with respect tothe output member.

10. The aircraft rotor structure of claim 9 in which the base portion ofthe hub structure has a central hub with diametrically opposite radialspokes unitary there with;

the two relatively rigid arms being unitarily joined to the outer endsrespectively of the two spokes;

each of the two rigid arms connecting one trunnion of one trunnion pairwith one trunnion of the other trunnion pair;

a flexible web interconnecting the two rigid arms;

said spokes being resilient to torsional forces, and

said web being resilient to bending forces,

whereby the rigid armsare permitted to rock with respect to the centralhub in providing relative rota tional movement between the trunnionpairs and relative rotational movement of each trunnion pair withrespect to the output member.

11. The aircraft rotor structure of claim 1 wherein said means to permitrelative rotational movement between the trunnion pairs includes: 1

a first inner drive shaft and a second outer tubular drive shaftsurrounding the inner drive shaft and concentric thereto;

the two shafts being united with the output member at their inner endsand extending from the output member;

each of the two shafts being connected at its outer end to a trunnionpair, and

at least oneof said shafts being resilient to torsional forces to permitrelative rotational movement between the trunnion pairs in relievingcoriolis forces resultingfrom teetering movement of the diametricallyopposite blades.

12. The aircraft rotor structure of claim 11 wherein each of the driveshafts is resilient in torsion to permit each trunnion pair to undergorotational movement relative to the other trunnion pair.

13. The aircraft rotor of claim 10 wherein the two drive shafts areconcentric torque tubes.

CUNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,784,319 Dated January 8, 1974 Inventor(s) Kenneth B. Amer et al It iscertified that error appears in the aboveidentified patent and that saidLetters Patent are hereby corrected as shown below:

The names of the joint inventors should read as follows:

Kenneth B. Amer; and Herbert T. Lund Signed and sealed this 30th day ofJuly 1974 (SEAL) Attest:

MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner; ofPatents F ORM Po-1oso (10-69) U.SY GOVERNMENT PRINTIN USCOlMM-DC 60376469

1. An aircraft rotor structure comprising: at least two pairs ofdiametrically opposite blades; an engine output member; at least twopairs of trunnions rotationally driven by the engine output member witheach pair of diametrically opposite blades pivoted on a trunnion pairfor teetering movement, and stress absorbing means interposed betweenthe output member and the pairs of trunnions to permit relativerotational movement between the trunnion pairs in relieving coriolisforces resulting from the teetering movement of the diametricallyopposite blades.
 2. The aircraft rotor structure of claim 1 wherein themeans providing relatIve rotational movement between the trunnion pairspermits relative rotational movement between each of the trunnion pairsand the engine output member.
 3. The aircraft rotor structure of claim 1wherein said means to permit relative rotational movement between thetrunnion pairs includes: a hub having a base portion which is relativelyrigid; said base portion being connected directly to the engine outputmember; arms formed integrally with the base portion with an armextending from the base portion to each trunnion pair; each arm havingsufficient strength to transmit rotational movement from said baseportion to a trunnion pair to provide rotational movement of thediametrically opposite blades pivotally connected to the trunnion pair,and at least one arm being sufficiently resilient to permit relativerotational movement of the trunnion pair to which the arm is connectedwith respect to the axis of the engine output member, whereby relativerotational movement between the trunnion pairs is permitted and alsorelative rotational movement of at least one trunnion pair with respectto the axis of the engine output member in reducing the transmission ofcoriolis forces to the engine output member.
 4. The aircraft rotorstructure of claim 3 wherein the connection of each arm to a trunnionpair is transverse to the plane within which the diametrically oppositeblades teeter with respect to the trunnion pair.
 5. The aircraft rotorstructure of claim 3 wherein each arm is sufficiently resilient topermit relative rotational movement of each trunnion pair relative tothe axis of the engine output member.
 6. The aircraft rotor structure ofclaim 4 wherein each arm is sufficiently resilient to permit relativerotational movement of each trunnion pair relative to the axis of theengine output member.
 7. The aircraft rotor structure of claim 3 whereina pair of arms extends from the base portion to each trunnion pair. 8.The aircraft rotor structure of claim 7 wherein the connections of eachpair of arms to each trunnion pair are transverse to the plane withinwhich the diametrically opposite blades teeter with respect to thetrunnion pair.
 9. The aircraft rotor structure of claim 1 wherein themeans providing relative rotational movement between the trunnion pairsincludes: a hub structure having a base portion driven by the outputmember and a pair of arms unitary with the base portion extending fromthe base portion to two trunnion pairs positioned on opposite sides ofthe axis of the output member, said arms being relatively rigid, andsaid base portion having sufficient strength to transmit rotationalmovement to the trunnion pairs but being resiliently deformable to allowthe two arms to tilt relative to the axis of the output member to permitthe trunnion pairs to undergo relative rotational movement and for eachtrunnion pair to undergo relative rotational movement with respect tothe output member.
 10. The aircraft rotor structure of claim 9 in whichthe base portion of the hub structure has a central hub withdiametrically opposite radial spokes unitary therewith; the tworelatively rigid arms being unitarily joined to the outer endsrespectively of the two spokes; each of the two rigid arms connectingone trunnion of one trunnion pair with one trunnion of the othertrunnion pair; a flexible web interconnecting the two rigid arms; saidspokes being resilient to torsional forces, and said web being resilientto bending forces, whereby the rigid arms are permitted to rock withrespect to the central hub in providing relative rotational movementbetween the trunnion pairs and relative rotational movement of eachtrunnion pair with respect to the output member.
 11. The aircraft rotorstructure of claim 1 wherein said means to permit relative rotationalmovement between the trunnion pairs includes: a first inner drive shaftand a second outer tubular drive shaft surrounding the Inner drive shaftand concentric thereto; the two shafts being united with the outputmember at their inner ends and extending from the output member; each ofthe two shafts being connected at its outer end to a trunnion pair, andat least one of said shafts being resilient to torsional forces topermit relative rotational movement between the trunnion pairs inrelieving coriolis forces resulting from teetering movement of thediametrically opposite blades.
 12. The aircraft rotor structure of claim11 wherein each of the drive shafts is resilient in torsion to permiteach trunnion pair to undergo rotational movement relative to the othertrunnion pair.
 13. The aircraft rotor of claim 10 wherein the two driveshafts are concentric torque tubes.